Lamp strings have been widely used in all kinds of celebrations and festivals. The lamp strings are attached to for example trees along a street. The lamp strings are powered by electricity and controlled by a controlling device to change the lighting status of the lamps.
Conventionally, the lamp strings are usually set to the full load condition without any time limits. Thus, a great consumption of power is encountered. Furthermore, to support such a great power consumption, a large-sized transformer is required. Therefore, the overall size of a lamp string controlling device may have a large size that is not suitable for outdoor use.
Furthermore, due to the large size of the power supply circuit, it is common that the power supply circuit and a control circuit are separated from each other with wires connected therebetween. This increases the cost and space requirement in installing the lamp string.
In addition, the lamp string controlling device is easily subject to electromagnetic interference. A high frequency filter may be connected between the power supply circuit and the control circuit to overcome the electromagnetic interference. The filter, however, increases the size and the cost of the lamp string controlling device.
Besides, the conventional control circuit may only control the lighting status of the lamp string in a limited ways. This is not consumer appealing.
It is thus desirable to have a lamp string controlling device that overcomes the above problems.